Control of particle size distribution in fluid coking of petroleum oils



Sept. 13, 1960 D. D. DUNLOP ET AL 2,952,356

CONTROL OF PARTICLE szzz DISTRIBUTION IN FLUID comm; OF PETROLEUM OILSFiled April 12, 1954 2 Sheets-Sheet 1 UNCLASSIFIED GAS souos FIGURE-Itor t PRODUCT or VAPORS GAS I3 I6 FEED I30 GAS 4 19 ooARsE K FROM HEATERFIGURE I I ELUTRIATING 22 17' GAS T TO HEATER 23 STEAM 1 t {w PRODUCTCOKE FIGURE JIE Donald D. Dunlop Robert S. Whiteley Inventors Werner A.Bauch By C4 Attorney Sept. 13,1960 D DUNLOP ETAL 2,952,356

CONTROL OF PAIRTICLEI SIZE DISTRIBUTiON IN FLUID COKING OF PETROLEUMOILS Filed 1954 2 Sheets-Sheet 2 I I INCLINED RECTANGULAR\% a g VERTICAL60 E 'RCULAR I a I (D 40 40 I I g 20 A E B 0 O 0 2O 4O 6O 80 I00 0 2OI00 INITIAL CHARGE WT. ON GIVENMESH 0 2O 4O 6O 80 I00 lo 0 2O 4O 6O 80I00 I I00 o M CASCADE r 80 so LOW CAPACITY- Q g S 60 g 60 L HIGHCAPACITY 40 g 40 2o 3 2o c I 0 0 IO I0 Fla-1&2

Donald D. Dunlop Roben S. WhiIeIey Inventors Werner A. Bauch y CM I YPatented Sept. 13, 1960 CONTROL OF PARTICLE SIZE DISTRIBUTION IN FLUIDCOKING OF PETROLEUM OILS Donald D. Dunlop, Werner A. Ranch, and RobertS. Whiteley, Baton Rouge, La., assignors to Esso Research andEngineering Company, a corporation of Delaware Filed Apr. 12, 1954, Ser.No. 422,438

3 Claims. (Cl. 209-136) This invention relates to the art of elutriatingsolids. It pertains to a method and apparatus for classifyingparticulate solids according to size. An application of this inventionis concerned with controlling the size distribution of finely dividedheat carrying solids used in hydrocarbon oil fluid coking systems.

Recently it has been proposed to coke hydrocarbon oils such as petroleumresidua by injecting them into a coking vessel containing a fluidizedbed of high temperature finely divided solids, e.g. coke, sand, spentcatalyst and the like. In the coking vessel, the oil undergoes pyrolysisin the fluidized bed, evolving lighter hydrocarbons and depositingcarbonaceous residue on the solid particles. The necessary heat for thepyrolysis is supplied by circulating a stream of the fluidized solidsthrough an external heater, generally a combustion zone, and back to thecoking vessel. The solids, which have had carbon deposited on themduring the coking, are partially combusted in the heater.

Among the problems exposed by the development of this fluid cokingprocess is one that apparently is peculiar to this type of operation,i.e., the problem of counteracting the particle size growth of thecirculating solids in the coking system. Because more carbon is producedby the coking process than is required to be burnt to supply heat, theparticulate solids, usually coke produced in the process, continue togrow by reason of the carbon depe osit-ion on them to the extent ofbecoming diflicult to fluidize or nonfluidizable.

It has been found necessary to add to the coking system, small sizeparticles to act as seeds or nuclei for the normal growth process and tomaintain an optimum size distribution of the particles. The productionof these seed particles necessitates expensive solids size reductionfacilities. By application of the method of this invention, the cost ofcreating seed particles is reduced considerably.

The present invention is concerned with the control of particle size anddistribution of the coke particles in a hydrocarbon oil fluid cokingsystem, whereby the operability of the fluid coking process is improved.

An excess of coke is produced by the coking process and is removed,according to the present invention, as selected coarse particles bymeans of an improved elutriation system. By the method of thisinvention, fine particles are preferentially retained in the cokingvessel thereby reducing the amount of seed coke that must be supplied tothe coking system and maintaining an optimum particle size distribution,thus achieving optimum coker performance.

Broadly, however, the invention is applicable to any process wherein itis necessary to classify solids. As an example of another application,it has been suggested to .use in fluid hydroforming operations for theproduction of gasoline an inert heat carrying material substantiallyheavier than the catalyst. This shot is circulated from a heating vesselto the vessel containing the fluidized catalyst and falls through thebed, giving up heat to the reaction. The shot is then separated andrecycled to the heater. This invention is particularly suited toseparating the shot from the catalyst prior to its return to the heater.

An object of this invention is to provide the art with an improvedmethod for elutriating and classifying particulate solids. It is aspecific object of this invention to decrease the seed coke requirementsof a residual oil fluid coking process and to enhance a balancedparticle size distribution in such a process by means of an. improvedsolids-gas elutriation system. These and further objects will becomereadily apparent as the drawings, forming a part of this specification,are discussed in detail.

In the drawings,

Figure 1 illustrates diagrammatically a system adapted to achieve theobjects of the present invention.

Figure 2 shows alternate sectional views taken along the line A-A ofFigure 1.

Figure 3 depicts schematically a modification of the invention appliedto a fluidized solids system for the coking of heavy petroleum oils.

Figure 4 graphically presents data illustrating the advantages of thisinvention.

Generally, the objects of this invention are attained by passing amobilized mass of particulate solids through a narrowly confinedinclined substantially unobstructed path in countercurrent flow to anascending gasiform medium, whereby the finer particles of the mass aresegregated and conveyed upwardly and the coarser particles passdownwardly. Control of the degree of elutriation is obtained by controlof the degree of inclination of the path, the length of the path and thevelocity of the elutriating gas. A more complete segregation of thesolids is obtained by passing the solids through a series of inclinedpaths, separated by vertical sections which act as mixing chambers. Theangle of inclination of the path is from 1 to 60 from the vertical,preferably, 30 to 60, and it is also preferred to have a flat or planesurface on the lower side of the inclination as a surface upon whichdescending solids slide.

The more particular objects of this invention are achieved by applyingthe invention to a vessel adapted to the fluid coking of particulatesolids. Specifically, a portion of the fluid solids bed within a coking;vessel is withdrawn, elutriated and the fines returned to the vesselwhile the coarser coke from the elutriation is withdrawn as product.

It will be seen that the present invention is distinguishable fromconventional elutriation or classification systerns. In conventionalelutriation systems, the solids are classified while greatly dispersedor diluted by the aerating medium. According to the present invention,the solids move downwardly in the dense phase while the aerating mediumstrips from the dense phase interface the finer particles and entrainsthem.

Referring now to the drawings, there is shown in Figure 1 a system forsegregating solids. The solids are introduced by line 10 into aninclined conduit 11. The particulate solids may be of varying densitiesbut it is contemplated that the invention will be applied to theclassification of solids of substantially uniform unit density. Thisinvention is applicable to particulate solids like coke, sand, catalyst,etc. or mixtures thereof.

At the lower end of the conduit a receiver 12 or expanded settling zoneis used to collect the coarser particles and line 4 is used to removethem from the receiver.

At the upper end of the conduit a solids-gas separator 5 or cyclone isused to remove the finer particles from the elutriating gas. Gas isremoved overhead by line '6 and the fines are transferred by line 7 to ahoppers from which they are removed by line 9.

Elutriating gas may be admitted near the base of the conduit or intohopper 12 by line 13, as is shown. Alternately, gas may be admitted byline 13a to the hopper to serve to fluidize the solids therein and thenmay be passed upwardly through conduit 11 to serve as elutriating gas.Any suitable gas may be used, e.g. steam, air, inert gases, etc. It maybe desirable in certain instances to use a gas that reacts, eitherchemically or physically, with the solids.

The velocity of the gas in the conduit will, of course, depend upon thesize and weight of the particles being classified, the density of thegas, the angle of inclination and the degree of elutriation desired. Forparticles having a size less than 500 microns, the superficial velocityof the gas in the conduit may vary from 2 to feet per second, preferablyfrom 2 to 6 f./s., for classifying particulate coke at an elutriatorangle of about 30 from the horizontal.

In Figure 2, alternate views of the inclined conduit are shown. Althougha circular pipe, as is shown in view A, will operate satisfactorily, arectangular pipe is preferred, shown in view B. In high pressureoperations, it is advantageous to retain the strength of a circular pipebut modify it by inserting a flat plate 14 or slide in the lower portionof the pipe. This arrangement is shown in view C.

The basic principle of the present invention is that the solids beingclassified slide down the bottom of the inclined conduit in a densephase, while countercurrent streams of gas strip fine particles ofl thetop of the dense phase. This is quite analogous to a countercurrentstripper.

When circular conduits are used, the ratio of the cokegas interface tothe coke rnass decreases with increase in pipe diameter. Henceelutriation efficiency decreases with increasing pipe diameter.Therefore, it is a preferred feature of the present invention to have aflat bottom surface in the lower portion of the inclined elutriatingconduit to promote elutriation efficiency.

Also, it is preferred to use a multiple or cascade arrangement of theinclined elutriating conduits as this promotes the movement of solidswithin the sliding solids mass and more readily causes fines to bebrought to the solids-gas interface. Other mixing devices or bafflingarrangements may be used to promote this agitation of the solids mass.

The mobility of the sliding solids and the capacity of the conduit maybe increased by a small amount of aeration of the solids. Thus, thebottom of the inclined conduit, or a portion thereof, may be composed ofporous micro metallic metal, and aerating gas passed through it.

Figure 3 illustrates another form of the inclined elutriator of thisinvention used in combination with a petroleum oil fluid coking vessel.

The art of \fluid coking is well known and for this reason only a briefdescription of the coking operation will be made. The oil to besubjected to pyrolysis is injected into a coking vessel 15 by line 16where it contacts a fluid bed of particulate solids, e.g. coke producedin the process. The fluidity of the bed is maintained by admitting steamto the base of the vessel by line 17. The reaction temperature of thebed is maintained at about 900-1600 F. by continuously withdrawing aportion of it by line 18 and transferring it to an external heater, e.g.combustion zone, and back, via line 19.

The injected oil undergoes pyrolysis evolving substantial amounts oflighter hydrocarbon vapors, removed by line 20, and depositing coke onthe particulate solids.

To remove the excess coke from the process, a portion of the fluid bedis withdrawn from the vessel by line 21, composed of a multiplicity ofinclined and vertical sections having fiat bottoms. The solids flowdownwardly in countercurrent flow to steam. Finer particles areselectively removed from the solids by the steam and are returned to thecoking vessel.

The coarse solids then enter a hopper 22 from which they are removed byline 23 as product. Steam is admitted to the hopper by line 24 inamounts sufficient to obtain the desired degree of segregation. Thissteam may be admitted to the base of the hopper to fluidize the solidstherein before being used for elutriation.

Although the solids flow rate may vary considerably, it is preferred tointroduce solids into the inclined pipe at a rate of 1000 to 5000lb./hr.-ft. to obtain optimum performance. 'For coke under approximately500 microns in size, the preferred rate is 1000 to 300.0 lb./hr.-ft. Theinvention is operable, however, at any rate below 1000 lb./hr.-ft.

As an alternate, the inclined conduit may be connected to the cokingvessel so as to remove solids from the dilute phase above the interfaceof the dense fluidized solids bed. This results in some sacrifice inthroughput but a much finer separation is made.

It has been found that the sharpness of the separation increases veryrapidly as the rate of solids flow decreases. However, the optimum rateis determined by economic considerations involving line size and gasrate.

Further, it has been found that it is desirable to have a length overcross-sectional height ratio for the inclined conduit of at least 2 inorder to allow sufficient time for the stripping action to occur.

The following examples are given to further elucidate this invention. A0.622" I.D. pipe, 0.7 foot long, was connected to a vessel containing abed of fluidized particulate solids, as in Figure 3, at a 30 angle fromthe vertical. Elutriation Was accomplished at gas, e.g. air, velocitiesbetween 4 and 8 feet per second and about 2 lbs. of solids werewithdrawn per hour. Table I illustrates the extent of the elutriationobtained:

Table 1 Original Elutriated Percent on Mesh Coke Coke Mixture Figure 4-Acompares this data with that obtained from a vertical dispersed phaseelutriator, 4.03 I.D., 11 feet long, handing about 1000 lbs./hr.-ft. atgas velocities of 9 to 11 feet/ second. It is readily apparent thatinclination of the path of elutriation greatly increases the efiiciencyof the separation.

Figure 4-B illustrates the benefits derived from the use of anelutriator the lower portion of which is a flat surface. The data forthe circular elutriator were obtained from a conduit 1 I.D., 4 /2 ft.long, inclined 30 from the vertical and handling 1970#/hr.-ft. of solidsat an elutriating gas velocity of 7.5 feet/second. The data for thefiat-bottomed conduit were obtained from a rectangular conduit 2" wide xdeep, 5 feet long,

inclined 30 from the vertical and handling 2000#/hr.- ft. at anelutriating gas velocity of 6.5 feet/second. Laboratory tests show a 6%to 12% improvement in particle size segregation of the on 48 and on 60mesh material when using a fiat-bottomed conduit as compared to acylindrical-bottomed vessel.

Figure 4-C illustrates that better elutriation is attained with acascade arrangement (see Figure 3), e.g. a series of inclined sectionsseparated by substantially vertical sections that act as mixing stages.The data for the cascade arrangement were obtained from a conduit 1" OD.handling 3200i/hr.-ft. of solids at a gas velocity of 7.1 tit/second.Four sections, having a total length of 3% feet, were used and wereinclined 30 f-romthe vertical. The inclined portions were separated byvertical sections 2 feet long. The data for the straight section wereobtained from a 1'' OD. pipe, 6 feet long, handling 2620#/hr.-ft. at agas velocity of 6.8 feet/ second.

Figure 4-D illustrates the advantages obtained by operating at lowerthroughputs. Both curves were obtained from an elutriator inclined 30from the vertical. The low capacity curve was obtained at a gas velocityof 5.7 feet/second and a solids rate of 156 lbs./hr.-ft. The highcapacity curve was obtained at a gas velocity of 4.7 feet/second and asolids rate of 1890 lbs./hr.-ft. It can be seen that the sharpness ofthe separation increases with decreases in capacity.

It should be noted that this invention is susceptible to manyvariations. As examples, it is feasible to arrange inclined elutriatingconduits in parallel or multiple arrangements. Or, the inclined sectionsmay be arranged in a staggered fashion such that the materialalternately flows in one direction and then the other. Thus, thepreviously described vertical mixing sections may be dispensed with.

Further, the angles of inclination of the inclined sections in a cascadearrangement may be varied. By having the angle of inclination greater atthe top of the cascade system, the efiect of surging in the system isminimized. For either a cascade or straight inclined elutriator, thecross-section area of the conduit may be varied. Thus a reduction ofabout 20% in the area at the bottom of the elutriating conduit helps toinsure that fines will not be withdrawn with the coarse product.

Other variations of the present invention and applications of it will beapparent to those skilled in the art.

Having described the invention, what is sought to be protected byLetters Patent is set forth in the following claims.

What is claimed is:

1. A method for classifying fluid coke particulate solids of sizes underabout 500 microns in diameter according to size which comprises, passingsaid solids at a rate in the range of 1,000 to 5,000 lbs. per hour persquare foot as a series of inclined confined dense phase streams eachhaving a defined upper surface and arranged one above the other inspaced vertical relation, said confined dense streams having aninclination in the range of 30 to 60 from the vertical and in the samedirection, passing the dense phase stream from one inclined level to thenext lower level through a vertical mixing zone in contact with a gas toform a gas-solids mixture passing to the next dense phase stream,introducing an elutriating gas into the outlet end of the bottomconfined dense stream for passage upwardly through said series ofinclined dense phase streams at a velocity in the range of 2 to 10 feetper second countercurrent to the downfiowing solids to strip fine solidsfrom the surface of said dense phase solids streams and upwardly throughsaid vertically disposed mixing zones to form gas-solids mixturestherein, withdrawing said gas and a substantial portion of fine solidsfrom the upper end of said series of inclined confined dense streams andremoving coarse solids from the outlet end of the bottom inclinedconfined dense stream.

2. The method of claim 1 wherein the inclination of said series ofinclined confined dense phase streams decreases from its top to bottomportions thus minimizing the effect of surging in the system.

3. An apparatus of the type described for elutriation of particulatesolids by a gas which includes a series of flat bottomed unobstructedelutriating conduits inclined 30 to from the vertical and each conduithaving a minimum length to cross-sectional height ratio above 2, saidconduits being arranged in cascade relation and inclined in the samedirection, a plurality of vertically disposed pipes, the lower end ofeach conduit being connected to the upper end of the next adjacentconduit by one of said vertical pipes each of which acts as a mixingchamber between said conduits, said top conduit being adapted todischarge fine particulate solids entrained in said gas from its upperportion and said bottom conduit being adapted to discharge coarseparticulate solids from its lower portion, means for admittingunclassified particulate solids to the upper portion of said topelutriating conduit for downward passage through said elutriatingconduits and pipes and an inlet conduit for admitting said gas to theinlet of said bottom elutriating conduit for upward passage through saidseries of elutriating conduits and pipes.

References Cited in the file of this patent UNITED STATES PATENTS1,332,751 Polo Mar. 2, 1920 1,545,055 Lindhard July 7, 1925 1,861,248Stebbins May 31, 1932 2,039,645 Hechenbleikner May 5, 1936 2,328,568Maxwell et al. Sept. 7, 1943 2,362,270 Hemminger Nov. 7, 1944 2,445,328Keith July 20, 1948 2,661,324 Lefier Dec. 1, 1953 2,728,632 MathesonDec. 27, 1955 2,766,185 Pansing Oct. 9, 1956

1. A METHOD FOR CLASSIFYING FLUID COKE PARTICULATE SOLIDS OF SIZES UNDERABOUT 500 MICRONS IN DIAMETER ACCORDING TO SIZE WHICH COMPRISES, PASSINGSAID SOLIDS AT A RATE IN THE RANGE OF 1,000 TO 5,000 LBS. PER HOUR PERSQUARE FOOT AS A SERIES OF INCLINED CONFINED DENSE PHASE STREAMS EACHHAVING A DEFINED UPPER SURFACE AND ARRANGED ON ABOVE THE OTHER IN SPACEDVERTICAL RELATION, SAID CONFINED DENSE STREAMS HAVING AN INCLINATION INTHE RANGE OF 30* TO 60* FROM THE VERTICAL AND IN THE SAME DIRECTION,PASSING THE DENSE PHASE STREAM FROM ONE INCLINED LEVEL TO THE NEXT LOWERLEVEL THROUGH A VERTICAL MIXING ZONE IN CONTACT WITH A GAS TO FORM AGAS-SOLIDS MIXTURE PASSING TO THE NEXT DENSE PHASE STREAM, INTRODUCINGAN ELUTRIATING GAS INTO THE OUTLET END OF THE BOTTOM CONFINED DENSESTREAM FOR PASSAGE UPWARDLY THROUGH SAID SERIES OF INCLINED DENSE PHASESTREAMS AT A VELOCITY IN THE RANGE OF 2 TO 10 FEET PER SECONDCOUNTERCURRENT TO THE DOWNFLOWING SOLIDS TO STRIP FINE SOLIDS FROM THESURFACE OF SAID DENSE PHASE SOLIDS STREAMS AND UPWARDLY THROUGH SAIDVERTICALLY DISPOSED MIXING ZONE TO FORM GAS-SOLIDS MIXTURES THEREIN,WITHDRAWING SAID GAS AND A SUBSTANTIAL PORTION OF FINE SOLIDS FROM THEUPPER END OF SAID SERIES OF INCLINED CONFINED DENSE STREAMS AND REMOVINGCOARSE SOLIDS FROM THE OUTLET END OF THE BOTTOM INCLINED CONFINED DENSESTREAM.